Hello Guest it is March 28, 2024, 07:10:07 AM

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - scoobystu

Pages: « 1 2 3 »
11
Success! I increased the acceleration to 1100 and now have much improved circles. There is still a wee bit of a flat area at one point which is 0.3mm smaller overall. I think I can live with that for the time being, with a bit more testing I will see if it is consistent. Now that I think about it I was getting the wobble when the 90deg corners were being cut in tiny radii so I might be able to increase the acceleration further.

Changed the e-stop pin to 11.

There is still a wee stutter in certain places which seems a bit strange. I was cutting large smooth arcs today and at the transition point where the arc is split there is a a slight hesitation and then it carries on. Is it seeing that there is a join in the arc and thinking about it? Is that a characteristic of stepper motors? The look ahead is set to 200 lines as recommended by mach handbook.

I realise that I may be barking up the wrong tree here but would a smooth stepper improve the performance?

12
Stirling, I did notice a distinct drop in speed when I put the kernel speed down. I should be able to bump the acceleration up a fair bit. When I was having trouble with 90deg corners I ended up putting the acceleration up to about 1200mm/s^2 to get it to cut sharp corners but seeing as I had started at 500 I thought it was a bit much. When I changed to the arc post processor I put the acceleration back to 500. I noticed that when the acceleration was at 1200 during cutting squares there was a wee bit of bounce after each corner so I suppose a safe acceleration would be about 1000? I did try a circle with the acceleration at 600 but it made no difference. I will increase the acceleration tomorrow. This may sound like a silly question but is the deceleration value the same as the acceleration value?

With respect to the e-stop pin. It was set to 10 or 11 I can't remember off hand which is the same as the Z zero plate. Every time I tried to zero the tool I got an e-stop. Someone suggested changing it to pin 2. I take it this is what you are talking about? Someone also said that I could assign pin 7 or 8  to the zero plate and leave the e-stop where it is. The first method worked and I left it for the time being until I tested other things. Should changing the zero touch plate to pin 7 or 8 work. If so I will do that as I would prefer that the e-stop system worked properly! 

Thanks very much for your help.   

13
I changed the kernel speed to 25kHz and it has slowed the machine down a bit but hasn't solved the issue.

XML file attached I hope.

14
The radio button in the general config is checked for CV. I take it that it will be on by default unless otherwise instructed by the Gcode?

I will have to wait until I am next at my machine to get the xml file.

Having re-read the Mach3 install document I see that a kernel speed of 35kHz is recommended for stepper motors mine is set to 45kHz. Would that make a difference?

15
Thanks stirling, How can I check that CV is working properly? As I mentioned previously I was having CV issues with rounding of 90 deg corners until I changed to using a post processor with arcs. I have tried to change CV settings to see if that made any difference but I have gone back to clearing all the CV check boxes in the config.

A bit more info that I forgot to add is that I have been speaking with someone who has an almost identical machine to mine and is also running Mach3. His machine will cut circles using arcs without a problem and he has sent me a few files which he has tested with good results at his end but do not work on my machine. Tried using Vectric to generate the G Code to make sure Artcam wasn't doing something weird but I am still having the flat spot issue.

The most annoying thing is that I know it can cut good circles just not with arcs at the moment!!

16
Thanks Rich, I was considering that it could be a calculation error but it is translating into a large error at the machine for some reason. I will measure backlash but not sure how I could measure flex. I have tried cutting 2mm deep circles but with the same result. I was cutting the full thing out to fit into a hole as it was easier to see the error.

I know that this will probably not cure the problem but I have been looking into smooth steppers. I have also noticed that during engraving the machine is very jerky which is causing it to vibrate. Would a smooth stepper help this and possibly help my circle issue. What would be a good smooth stepper to buy and are they easy to install for a newbie?

Could there be a mismatch between my computer and the kernel speed that mach is set to? How do you determine the correct kernel speed to run at with respect to the PC?

Gary, I tried changing the setting to beziers but it made the problem worse, I got 12 flat spots rather than 4.....

Stu

17
I hope this image has made it onto the thread. If not here is a link to it. http://clachanwood.wordpress.com/?attachment_id=818

It is quite hard to see the problem on it's own so I have fitted the dodgy circle into a circular rebate I did using a post processor without arcs.


The code I used is as follows, for the defective circle.

G17
G0Z12.400
G0X0.000Y0.000S18000M3G04P15
G0X-78.000Y-0.000Z12.400
G1Z-4.650F5100.0
G3X0.000Y-78.000I78.000J-0.000F9900.0
G3X78.000Y0.000I0.000J78.000
G3X0.000Y78.000I-78.000J0.000
G3X-78.000Y-0.000I0.000J-78.000
G1Z-9.300F5100.0
G3X0.000Y-78.000I78.000J-0.000F9900.0
G3X78.000Y0.000I0.000J78.000
G3X0.000Y78.000I-78.000J0.000
G3X-78.000Y-0.000I0.000J-78.000
G1Z-13.950F5100.0
G3X0.000Y-78.000I78.000J-0.000F9900.0
G3X78.000Y0.000I0.000J78.000
G3X0.000Y78.000I-78.000J0.000
G3X-78.000Y-0.000I0.000J-78.000
G1Z-18.600F5100.0
G3X0.000Y-78.000I78.000J-0.000F9900.0
G3X78.000Y0.000I0.000J78.000
G3X0.000Y78.000I-78.000J0.000
G3X-78.000Y-0.000I0.000J-78.000
G0Z12.400
G0X0.000Y0.000
G0Z12.400
M05
G0X0.000Y0.000
M30

18
My main query would be why will it cut an exact circle if I am not using a post processor with arcs but when I use arcs I get flat spots. The flat spots are consistently about 1mm smaller overall on any circle when using an arc post processor.

19
I had a feeling that backlash may be mentioned. Having read a few other similar posts that seemed to be the culprit. I will need to see if I can find a dial gauge.

20
Hi there,

I am new to CNC and mach3 and am in the process of setting up a machine that I bought for woodwork. I previously had a problem with getting accurate 90 deg corners (without rounding) with CV on but that was resolved by changing to a post processor using arcs. The problem I now have is that when cutting circles using the arc method (I am using artcam which turns circles into 4 adjoined arcs) at each point where one arc ends and another begins I get a flat spot. Previously using the post processor that I think converted it to absolute coordinates the circles were spot on. Equally when I tried the Mach3 circle wizard again it was accurate even although it also uses arcs, the crucial difference being that it creates one 360 deg arc.

The work around I have at the moment involves using two different post processors if cutting circles or if I am cutting square shapes with artcam. I would be very grateful if someone who has experienced this before could point me in the right direction. In an ideal world I would only have to use one post processor to cut out the job in one go. Or is there a setting in Mach that allows for the fact that circles have been split into 4 arcs and compensates when it cuts them out.

Any help would be appreciated.

Stu

Pages: « 1 2 3 »